Assignment:
Learning Objectives
1. Write an overall summary of photosynthesis, using only the terms carbon dioxide, chlorophyll, light, oxygen, sugar, and water.
2. Summarize the events of the light-dependent and the light-independent reactions of photosynthesis.
3. Explain the significance of the absorption spectrum of chlorophyll a relative to energy utilization in photosynthesis.
4. Know all the terms in bold print in the Introduction.
Materials
• 2 test tubes in a glass
• 2 straws
• 150 watt lamp
• large glass
• aluminum foil
• metric ruler
• Elodea
• 3% sodium bicarbonate
• distilled water
Instructions
Do the lab on photosynthesis found after the assignment below.
- Be careful with the light - it is very HOT!
- Instead of using the test tube clamp to hold the ignition tubes, you will need to sit them in a glass.
- Instead of using a rubber stopper and bent glass for the test tubes, do the following: cut the straw about 2 inches below the bent elbow. Then fill the test tube full of the specified liquid, then make an aluminum stopper around the straw. Put the aluminum stopper and straw in the test tube making sure there is no air bubble.
Assignment
Complete the postlab questions on the photosynthesis lab after this page in the syllabus.
Postlab questions must be typed and saved as a document with no spaces or special characters in the filename before submitting them in WebCT for a grade. Make sure you include each question before you type the answer.
Observing Oxygen Evolution During Photosynthesis
Supplies:
• 2 test tubes
• 2 pieces of aluminum foil
• 2 straws
• 150 watt lamp
• large clear glass
• marker
• ruler
• 2 sprigs of Elodea (anachris- plant found in fish tanks)
• 3% NaHCO3
• distilled water
Methods:
• Place a generous amount of Elodea (cut side up; make sure cuts are fresh) in each test tube. Mark the test tubes 1 and 2.
• Fill tube 1 with 3% NaHCO3 solution and fill tube 2 with distilled water. Cut the bent end of the straw so that you have an "L" shape about 1 - 1½ long on one end and 4 inches long on the other. Make a stopper to secure the straw into the tube making sure the long end is hanging out horizontal. Make sure there is enough solution in each tube so that when you insert the aluminum foil in a stopper, the solutions rise to about ¼ the length of the straw. Mark the locations of the solutions on each straw. Place the test tubes side by side in a clear container or prop them up against something.
• Fill the large clear glass with tap water and place it between the lamp and test tubes. The tubes, large glass and lamp should be as close together as possible.
• Turn the lamp on and when the solution in either straw starts to move, begin timing the reactions in both tubes for 10 minutes. Do not bump the straw or readjust the stopper or you will alter your readings. At the end of 10 minutes, mark the distance the solutions traveled on each tube and turn off the light.
• Immediately wrap each test tube completely with aluminum foil and begin timing for another ten minutes while the solutions recede. After 10 minutes, mark the receding edge of the solutions.
• Measure the distance the solutions traveled while the light was on and record in the table. This is the net photosynthesis (mm/10 min).
• Measure the distance the solutions receded while the light was off and record in the table. This is aerobic cellular respiration (mm/10 min).
On your own paper answer the following:
1. Results from the table and perform the calculations.
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Estimates
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Tube 1
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Tube 2
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net photosynthesis
(mm/10 min x 6)
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aerobic respiration
(mm/10 min x 6)
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gross (total) photosynthesis
(mm/10 min x 6)
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2. What difference, if any, was there between the results in Tube 1 and Tube 2?
3. Why was there such a difference?